1. Field of the Invention
The present invention relates to a solid-state image-sensing device. More particularly, the present invention relates to a charge coupled device (CCD) solid-state image-sensing device.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional color solid-state image-sensing device system 100 using a conventional CCD solid-state image-sensing device 120. Referring to FIG. 1, the color solid-state image-sensing device system 100 includes a controller 110, the CCD solid-state image-sensing device 120, an interpolator 130, and a signal processing unit 140. The color solid-state image-sensing device system 100 is applied in, for example, a mobile phone and a digital still camera. The CCD solid-state image-sensing device 120 senses visible images, converts the images into electrical signals, and periodically generates color image data (red, green, and blue). The controller 110 generates vertical driving signals and horizontal driving signals to drive the CCD solid-state image-sensing device 120. The three-color (red, green, and blue) signals R, G, and B are interpolated by the interpolator 130. The interpolated three-color signals R, G, and B are output as Vout to and displayed on a display device, e.g., a liquid crystal display (LCD), via the signal processing unit 140.
Particularly, the solid-state image-sensing device 120 includes photodiodes arranged in a two-dimensional matrix, a vertical CCD (not shown) for transmitting electric charge packets vertically while connected to each photodiode, and a horizontal CCD (not shown) for receiving the electric charge packets output from the vertical CCD and transmitting them horizontally. The vertical CCD is controlled by the vertical driving signals and transmits the electric charges generated by the photodiodes vertically to the horizontal CCD. The horizontal CCD is controlled by the horizontal driving signals, which are generated by the controller 110, and receives the electric charge packets output from the vertical CCD and transmits them horizontally.
The driving of the CCD solid-state image-sensing device 120 is usually composed of, e.g., a vertical drive of tens of kHz, a horizontal drive of tens of MHz, a reset drive for the output, applications of other bias voltages, etc. The vertical drive needs a separate driving circuit because the voltage level required by the vertical drive is different from the output level of a typical logic circuit. The horizontal drive uses a conventional buffer logic circuit in a simple pull up-pull down form. FIG. 2 is a block diagram of a horizontal CCD driving circuit 200 of the CCD solid-state image-sensing device 120 of FIG. 1. Referring to FIG. 2, the horizontal CCD driving circuit 200 in the controller 110 typically generates at least two horizontal driving signals H1 and H2 to maximize transmission efficiency. That is, the at least two horizontal driving signals H1 and H2 with different logic states from each other are generated at inverters 201, 202 and 203 from a clock signal XH for driving the horizontal CCD.
When the CCD solid-state image-sensing device 120 is to be adopted in small mobile devices, e.g., mobile phone cameras or digital still cameras, reducing power consumption becomes more critical. To solve this problem, bias voltage and current of an amplifier at the output end have been reduced. However, in the case of the horizontal drive, an increase in capacitance corresponding to an increase in the resolution of the CDD solid-state image-sensing device 120, and overall power consumption of the same, continue to increase. The capacitance of the CCD solid-state image-sensing device 120 is hundreds to thousands of pF, and an alternating current (AC) for repeatedly charging and discharging the capacitance during operation is a major cause of power consumption when the operating frequency is high. In this case, the power consumption Pø, which depends on the driving signal, can be represented by Equation (1) below. In Equation (1), f is driving frequency, C is capacitance, and V is voltage amplitude.Pφ=f×C×V2  (1)
In the vertical CCD drive of the conventional CCD solid-state image-sensing device 120, the operating frequency is about 10-20 kHz, the capacitance is about 500-2000 pF, and the voltage amplitude is about 5-10 V. Accordingly, the power consumption is in the range of 0.12-4 mW. In the horizontal CCD drive, the operating frequency is about 8-40 MHz, the capacitance is about 10-50 pF, and the voltage amplitude is about 3-5 V. Accordingly, the power consumption is in the range of 0.72-50 mW. Thus, the power consumption of the horizontal CCD drive is higher than the vertical CCD drive, and tends to incrementally increase as the resolution increases. In the CCD solid-state image-sensing device 120 designed to be integrated into small mobile devices, the very end driving voltage of an amplifier at the output end has been reduced from 12-15 V to 5 V, which reduces the overall power consumption to 73 mW. However, the power consumption in the horizontal CCD drive is around 37.4 mW, thereby consuming about 50% of the total power.
A method of reducing the power consumption in the horizontal CCD drive by the driving signals of opposite from each other includes three devices, which perform switching operations, between a driving signal outputting unit and a horizontal CCD. Connection of driving signals is open while they are being inverted into another logic state, and signal lines are equipotentialized. However, when signals to open the connection of the driving signals and signals to equipotentialize the signal lines are simultaneously applied, a switch for equipotential may be connected while the connection of the driving signal is not completely open due to the difference in time each switch needs to respond. Here, power sources are short-circuited through output buffers. Accordingly, in the output buffers, high current instantly flows through the switch for the equipotential. As a result, the power saved may be decreased, and, in the extreme, power consumption may even be higher than in the conventional technology.